[PATCH v2 1/3] gdb: add convenience variables around linker namespace debugging

Guinevere Larsen
2025-04-09T20:48:52Z

This commit adds 2 simple built-in convenience variables to help users
debug an inferior with multiple linker namespaces. The first is
$_active_linker_namespaces, which just counts how many namespaces have SOs
loaded onto them. The second is $_current_linker_namespace, and it tracks
which namespace does the current location in the inferior belongs to.

This commit also introduces a test ensuring that we track namespaces
correctly, and that a user can use the $_current_linker_namespace
variable to set a conditional breakpoint, while linespec changes aren't
finalized to make it more convenient.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
---
gdb/NEWS | 6 +++
gdb/doc/gdb.texinfo | 12 +++++
gdb/solib-svr4.c | 6 +++
gdb/solib.c | 43 +++++++++++++++
gdb/testsuite/gdb.base/default.exp | 2 +
gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c | 6 +++
gdb/testsuite/gdb.base/dlmopen-ns-ids.exp | 55 ++++++++++++++++++++
7 files changed, 130 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index 99ec392d4c4..053541683f1 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -40,6 +40,12 @@
namespace into which the library was loaded, if more than one namespace
is active.

+* New built-in convenience variables $_active_linker_namespaces and
+ $_current_linker_namespace. These show the number of active linkage
+ namespaces, and the namespace to which the current location belongs to.
+ In systems that don't support linkage namespaces, these always return 1
+ and [[0]] respectively.
+
* New commands

maintenance check psymtabs
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index b251c8e1228..2dda8abd407 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -13046,6 +13046,18 @@ variable which may be @samp{truecolor} or @samp{24bit}. Other color spaces are
determined by the "Co" termcap which in turn depends on the @env{TERM}
environment variable.

+@vindex $_active_linker_namespaces@r{, convenience variable}
+@item $_active_linker_namespaces
+Number of active linkage namespaces in the inferior. In systems with no
+support for linkage namespaces, this variable will always be set to @samp{1}.
+
+@vindex $_current_linker_namespace@r{, convenience variable}
+@item $_current_linker_namespace
+The namespace which contains the current location in the inferior. This
+returns GDB's internal identifier for namespaces, which is @samp{[[@var{n}]]}
+where @var{n} is a zero-based namespace number. In systems with no support
+for linkage namespaces, this variable will always be set to @samp{[[0]]}.
+
@end table

@node Convenience Funs
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 83cb389dad5..148359a0227 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -451,6 +451,12 @@ svr4_maybe_add_namespace (svr4_info *info, CORE_ADDR lmid)
info->namespace_id.push_back (lmid);

info->active_namespaces.insert (i);
+
+ /* Create or update the convenience variable "active_namespaces".
+ It only needs to be updated here, as this only changes when a
+ dlmopen or dlclose call happens. */
+ set_internalvar_integer (lookup_internalvar ("_active_linker_namespaces"),
+ info->active_namespaces.size ());
}

/* Return whether DEBUG_BASE is the default namespace of INFO. */
diff --git a/gdb/solib.c b/gdb/solib.c
index 4876f1a92ea..1ba98137f5e 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -1715,6 +1715,42 @@ default_find_solib_addr (solib &so)
return {};
}

+/* Implementation of the current_linker_namespace convenience variable.
+ This returns the GDB internal identifier of the linker namespace,
+ for the current frame, in the form '[[<number>]]'. If the inferior
+ doesn't support linker namespaces, this always returns [[0]]. */
+
+static value *
+current_linker_namespace_make_value (gdbarch *gdbarch, internalvar *var,
+ void *ignore)
+{
+ const solib_ops *ops = gdbarch_so_ops (gdbarch);
+ const language_defn *lang = language_def (get_frame_language
+ (get_current_frame ()));
+ std::string nsid = "[[0]]";
+ if (ops->find_solib_ns != nullptr)
+ {
+ CORE_ADDR curr_pc = get_frame_pc (get_current_frame ());
+ for (const solib &so : current_program_space->solibs ())
+ if (solib_contains_address_p (so, curr_pc))
+ {
+ nsid = string_printf ("[[%d]]", ops->find_solib_ns (so));
+ break;
+ }
+ }
+
+
+ /* If the PC is not in an SO, or the solib_ops doesn't support
+ linker namespaces, the inferior is in the default namespace. */
+ return lang->value_string (gdbarch, nsid.c_str (), nsid.length ());
+}
+
+static const struct internalvar_funcs current_linker_namespace_funcs =
+{
+ current_linker_namespace_make_value,
+ nullptr,
+};
+
void _initialize_solib ();

void
@@ -1727,6 +1763,13 @@ _initialize_solib ()
},
"solib");

+ /* Convenience variables for debugging linker namespaces. These are
+ set here, even if the solib_ops doesn't support them,
+ for consistency. */
+ create_internalvar_type_lazy ("_current_linker_namespace",
+ &current_linker_namespace_funcs, nullptr);
+ set_internalvar_integer (lookup_internalvar ("_active_linker_namespaces"), 1);
+
add_com (
"sharedlibrary", class_files, sharedlibrary_command,
_ ("Load shared object library symbols for files matching REGEXP."));
diff --git a/gdb/testsuite/gdb.base/default.exp b/gdb/testsuite/gdb.base/default.exp
index d4d6b208057..3abd0495387 100644
--- a/gdb/testsuite/gdb.base/default.exp
+++ b/gdb/testsuite/gdb.base/default.exp
@@ -699,6 +699,8 @@ set show_conv_list \
{$_gdb_minor = 1} \
{$_shell_exitsignal = void} \
{$_shell_exitcode = 0} \
+ {$_active_linker_namespaces = 1} \
+ {$_current_linker_namespace = <error: No registers.>}\
}
if [allow_python_tests] {
append show_conv_list \
diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
index 3bcd8196483..c7c038a08d1 100644
--- a/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
+++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids-main.c
@@ -41,6 +41,12 @@ main (void)
handle[2] = dlmopen (LM_ID_NEWLM, DSO_NAME, RTLD_LAZY | RTLD_LOCAL);
assert (handle[2] != NULL);

+ for (dl = 2; dl >= 0; dl--)
+ {
+ fun = dlsym (handle[dl], "inc");
+ fun (dl);
+ }
+
dlclose (handle[0]); /* TAG: first dlclose */
dlclose (handle[1]); /* TAG: second dlclose */
dlclose (handle[2]); /* TAG: third dlclose */
diff --git a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
index 03b7a527af5..8f5376fa3de 100644
--- a/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
+++ b/gdb/testsuite/gdb.base/dlmopen-ns-ids.exp
@@ -103,4 +103,59 @@ proc test_info_shared {} {
"after unloading everything"
}

+# Run all tests related to the linkage namespaces convenience
+# variables, _active_namespaces and _current_namespaces.
+proc_with_prefix test_conv_vars {} {
+ clean_restart $::binfile
+
+ gdb_test "print \$_active_linker_namespaces" "1" \
+ "1 namespace before starting inferior"
+ gdb_test "print \$_current_linker_namespace" "No registers." \
+ "No current namespace before starting inferior"
+
+ if { ![runto_main] } {
+ return
+ }
+
+ gdb_test "print \$_active_linker_namespaces" "1" \
+ "Before activating namespaces"
+ gdb_test "print \$_current_linker_namespace" ".*\"\\\[\\\[0\\\]\\\]\"" \
+ "Still in the default namespace"
+
+ gdb_breakpoint "inc" allow-pending
+ gdb_breakpoint [gdb_get_line_number "TAG: first dlclose"]
+
+ foreach_with_prefix dl {3 2 1} {
+ gdb_continue_to_breakpoint "inc"
+
+ gdb_test "print \$_current_linker_namespace" ".*\"\\\[\\\[$dl\\\]\\\]\"" \
+ "Verify we're in namespace $dl"
+ }
+
+ gdb_continue_to_breakpoint "first dlclose"
+ gdb_test "print \$_active_linker_namespaces" "4" "all SOs loaded"
+
+ gdb_test "next" ".*second dlclose.*" "close one SO"
+ gdb_test "print \$_active_linker_namespaces" "3" "one SOs unloaded"
+ gdb_test "next" ".*third dlclose.*" "close another SO"
+ gdb_test "print \$_active_linker_namespaces" "2" "two SOs unloaded"
+
+ # Restarting GDB so that we can test setting a breakpoint
+ # using the convenience variable, while a proper bp syntax
+ # isn't implemented for namespaces
+ clean_restart $::binfile
+ if {![runto_main]} {
+ return
+ }
+
+ # We need to load one SO because you can't have confitional
+ # breakpoints and pending breakpoints at the same time with
+ # gdb_breakpoint.
+ gdb_test "next" ".*assert.*" "load the first SO"
+ gdb_breakpoint "inc if \$_streq(\$_current_linker_namespace, \"\[\[2\]\]\")"
+ gdb_continue_to_breakpoint "inc"
+ gdb_continue_to_end "" continue 1
+}
+
test_info_shared
+test_conv_vars
--
2.49.0